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http://hdl.handle.net/1957/33962
2015-07-30T22:28:39ZTsunami and storm wave impacts on coastal bridges
http://hdl.handle.net/1957/56512
Tsunami and storm wave impacts on coastal bridges
Sieffert, Betsy Rose
Wave loads on coastal bridges due to tsunami and storm waves are studied through a set of laboratory experiments and numerical calculations. Effects of wave nonlinearity and entrapped air on wave loading under conditions where the bridge may be partially or fully inundated are of particular interest. In addition, effects of compressibility and scaling are investigated through numerical calculations. With the destruction of bridges during recent events such as the 2011 Tohoku tsunami and hurricanes Katrina in 2005 and Ivan in 2004, this highlights the importance of this research in understanding the mechanisms of failure during such events to prevent future coastal bridge failures. Destruction of these bridges is not only financially costly, but can prevent emergency services from reaching coastal communities, thus potentially contributing to loss of life. Along with the bridges, this research is applicable to other coastal and offshore structures, such as piers, submerged breakwaters and offshore platforms, in which wave loading or entrapped air is of concern. To investigate this problem, an extensive set of experiments is conducted on a flat plate, bridge model with girders, and a bridge model with varying percentages of trapped air that serves as a valuable benchmark for understanding wave loads on coastal structures, and bridges in particular. The wave cases tested include an extensive set of water depths, wave amplitudes and wave periods (for periodic waves) to cover a wide range of solitary and shallow-water to intermediate-water depth cnoidal waves. A range of model elevations was also tested to cover a range where the entire model is fully submerged below the water surface, to where the model is fully elevated above the water surface, and in the case of the model with girders, the girders are fully elevated as well. Experiments were conducted in a two-dimensional wave flume located in the University of Hawaii at Manoa's Hydraulics Lab in the Civil and Environmental Engineering Department. The models used were representative of a 1:35 scale model of a two-lane coastal bridge, typical in an island community. To study the effects of entrapped air, a series of experiments is conducted where side panels were added to each side of the model to trap air between the girders. Then different percentages of air-relief openings are added to the panels to capture a range of cases where no air can escape between the girders, to where all the air can escape and the wave can freely interact with the bottom of the bridge deck. Data from these experiments show the largest vertical uplift forces and forces in the direction of wave propagation on a flat plate and a bridge model occur when the structure is near the still-water level (SWL). For the cases where air is trapped, the addition of air relief openings significantly reduces uplift forces. Many current empirical relations estimating wave loads on coastal bridges only take hydrostatic effects into account. When compared with empirical estimations, data from these experiments show both hydrostatic and hydrodynamic forces must be taken into consideration. Comparison is also made with numerical calculations solving incompressible Euler's equations by use of the CFD software OpenFOAM, discussed in Hayatdavoodi (2013), Seiffert, Hayatdavoodi & Ertekin (2014), and Hayatdavoodi, Seiffert & Ertekin (2014b) with excellent agreement. Effects of compressibility and scaling are tested numerically by solving compressible and incompressible Euler's equations. Numerical calculations show that the effects of compressibility on the long duration forces are small. Calculations also show that when Froude scaling is applied to forces on the model scale, the forces agree well with force calculations at the prototype scale. These results have important design implications for bridge engineers.
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2014-01-01T00:00:00ZTopology, modeling and analysis of bridge of bridge DC-AC and AC-DC power converters
http://hdl.handle.net/1957/56509
Topology, modeling and analysis of bridge of bridge DC-AC and AC-DC power converters
Reed, Justin Kyle
The bridge of bridge converter (BoBC) topology is a recent addition to the family of power converters. Inherently modular and multilevel, the BoBC is also a flexible topology that employs "building blocks" for realizing power conversion throughout an extremely wide range of power, voltage, current and applications. However, its use has so far been extremely limited and its capabilities, limitations and fundamental behavior largely unexplored. This research therefore builds a generalized topological framework for the analysis and design of the BoBC, focusing on dc-ac and ac-dc power conversion. Using this framework, techniques for sizing converter components such as capacitors and switches are developed. Dynamic phasor modeling in dq coordinates suitable for multilevel converters of arbitrary size permits the use of time-invariant visualization and enables the use of the BoBC in high-performance applications such as motor drives. A case study laboratory-scale converter validates the predicted multilevel behavior, and computer simulations confirm model accuracy.
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2014-01-01T00:00:00ZAesthetic Womanist Pedagogy : A Case Study of Educative Emotional Everyday Latina Communicative Practices
http://hdl.handle.net/1957/56500
Aesthetic Womanist Pedagogy : A Case Study of Educative Emotional Everyday Latina Communicative Practices
Carrillo, Rosario
"In this study, I examine the ways that one group of Latinas use literacy, orality, and visual representations to communicate and teach their beliefs, values and visions to their children, families, friends, and community ... I turned to their Latina/o urban community in the Midwest. There I had the great fortune to learn from a remarkable Latina mother, Mrs. Carla Paula Villa, and people in her life. Together they have taught me about their everyday ways of knowing, doing and being--particularly about a set of artistic expressions used to beautify and teach -- and have expanded my way of viewing pedagogy. This study reports findings from a multiple-year investigation of the social and educative lives of Mrs. Villa and her network and draws conclusions about how literacy and general education theory and practice may be informed by a deep understanding of their practices. In particular, I highlight how Mrs. Carla Paula Villa's combinations of socially constructed forms of representation, aesthetic tastes and markers, and cultural traditions and innovations enables her to negotiate with style oppressive social and material conditions; and thus to model how to do so. Making this type of space available to Latina/o youth would temper the way schools fail them in the United States."--P. 1.
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2006-01-01T00:00:00ZThai Secondary School Students' Probability Misconceptions : The Impact of Formal Instruction
http://hdl.handle.net/1957/56492
Thai Secondary School Students' Probability Misconceptions : The Impact of Formal Instruction
Talawat, Puttoei
Probability is an important mathematics topic and is required for all Thai secondary school students. However, previous research found that both students and teachers often held several probability misconceptions, students had difficulties learning the topic, and teachers did not have sufficient knowledge to teach the topics. The purpose of this study was to investigate the types of probability misconceptions held by Thai secondary school students and their mathematics teachers, how the teachers implemented a nationwide inquiry-based curriculum, and how instruction impacted the students' understanding of the concepts. The participants were two grade 9 mathematics teachers and their students in four classes, 204 students in total. The data collection included lesson observations, a probability misconception pretest and posttest, and teacher interviews. The results showed that both the teachers and the students held several types of probability misconceptions. Even though the students' performance on the posttest was significantly improved after instruction, they still did not do well. The students learned knowledge on probability as evidenced in their responses on the posttest, but they were still having trouble appropriately applying the knowledge. Teachers' probability misconceptions and their understanding of probability topics affected how their students learned and understood probability.
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2015-01-01T00:00:00Z